Switch



Sept. 10, 1940.

w. J. UHLHORN 2,214,092

SWITCH Filed Oct. 26, less s SheetsSheet 1 Sept. 10, 19 w. J. UHLHORN SWITCH Filed 001;. 26, 1938 3 Sheets-Sheet 2 FZ E Sept. 10, 1940.

w. J. UHLHORN 2,214,092

SWITCH Filed Oct. 26, 1958 s Sheets-Sheet 3 Patented Sept. 10, 1940 UNITED STATES PATENT OFFICE 3 Claims.

This application is a continuation in part of my abandoned application, Serial No. 124,544,

filed February 8, 1937.

This invention relates to switches and more particularly to so-called flow switches.

In industrial practices there are many instances where a fluid is circulated through a system under suction conditions as where obnoxious into an oven or the like and there are other instances where a fluid is circulated through a system under suction conditions as where obnoxious fumes are withdrawn from vats in chemical processes or from ovens or also as where dust is withdrawn from grinding and polishing machines or the like. Heretofore switches have been disposed in the path of flow through such systems to interrupt the fluid flow under certain conditions or to be responsive to a failure in fluid flow and for other purposes. However, such switches have been responsive to either suction or pressure and it was not possible to use a pressure responsive switch with a suction system or a suction responsive switch with a pressure system, this being due to inherent features in the design of the switches. The supplier of such switches is not always conversant with the use to which the switch is to be put and it has often occurred that a switch wholly unsuited for the purpose for which it is intended has been furnished.

It has been proposed to overcome this condition by providing more or less intricate adjustments in switches of the aforesaid character to enable them to be arranged to be responsive to either pressure or suction, but such switches have been difficult to adjust, expensive to manufacture, and were otherwise objectionable. Hence the salient object of my invention is to provide a novel flow switch of simple and economical construction and efiicient and positive operation that may be expeditiously arranged to be responsive to either pressure suction (the term pressure being used herein with reference to pressure greater than atmospheric and the term suction being used herein with reference to pressure less than atmospheric).

In flow switches that have been employed heretofore, it has been observed that there is a tendency for the movable element of the valve or other pressure responsive means of the switch to vibrate relative to the fixed member whereby what is called chatter results, and another important object of my invention is to overcome such tendency to chatter in the control means of a flow switch.

Moreover, I have observed that, as in those instances where dust or the like passes through a system with which a flow switch is used, such dust or the like may collect on the pressure responsive parts and impair proper operation thereof, and in those instances where fumes pass through the system with which a flow switch is used, such fumes, particularly after the end of a period of operation, may congeal on the pressure responsive parts of the switch.

Therefore, still another object of my invention is to prevent dust or other foreign matter from collecting on operative parts of a flow switch and also to prevent fumes from congealing on such parts, and an object ancillary to this is to utilize a filter or condenser intermediate the operative parts of a flow switch and the source of fluid flow to such parts.

Further objects will be apparent from the following description wherein reference is made to the accompanying drawings in which:

Fig. 1 is an end elevation, taken on the line |I on Fig. 2, of one form of my novel switch;

Fig. 2 is a vertical sectional view taken substantially on the line 22 on Fig. 1 and showing the switch arranged for use with a pressure system;

Fig. 3 is a fragmentary vertical sectional view, similar to Fig. 2, and showing the switch arranged for use with a suction system;

Fig. 4 is a fragmentary detail view showing an alternative form of circuit making and breaking means that may be used in my switch;

Figs. 5 and 6 are vertical sectional views, similar to Fig. 2, but showing other forms of my invention;

Fig. '7 is a sectional detail view taken on the line 'll on Fig. 2; and

Fig. 8 is still another vertical sectional View, similar to Fig. 2, and showing another form of my invention.

In the form of my invention shown in Figs. 1 and 2 a substantially cylindrical housing H is provided which has an inwardly projecting rib R on the inner wall thereof. The rib R is positioned substantially midway between the ends of the housing H and provides a valve seat or stop against which a disc D is adapted to seat. The disc D is supported for movement toward and away from the valve seat by the arm 9 of a lever L fulcrumed substantially midway between its ends on a rod it) carried by the housing H, said arm 9 extending through an opening H in said housing.

The arm l2 of the lever L carries a saddle l3 in which a so-called mercury switch I4 is removably mounted, said switch comprising a closed tubular housing having a globule of mercury therein adapted to close the circuit between a pair of contacts as 55 located at one end of the tubular housing, the arrangement being such that when the lever L is tilted in one direction as, for example, to seat the disc D on the valve seat R, the globule of mercury closes circuit between the contacts as !5, but when the lever L is pivoted upon movement of the disc D away from the valve seat R, as into the broken-line position of Fig. 2, the globule of mercury runs to the other end of the enclosed tubular housing and thereby opens circuit between the contacts as Hi. It is, of course, to be understood that other forms of circuit making and breaking means may be substituted for the disclosed mercury switch.

A pad 56 is provided on the housing H about the opening ii and the bottom wall of a casing H is seated on and secured to this pad, said casing I? enclosing the mercury switch M. A suitable electrical connection fitting is provided at the upper end of the casing ii and electrical conductors (not shown) lead through the fitting l8 and are connected to electrical terminals as I9 in the casing ii, to which terminals flexible conductors as C are attached, these conductors C being connected to the contacts as i5. The electrical conductors that are to pass through the fitting is may be led to any suitable means adapted to be controlled by the switch, which means may be an audible or visible signal or the control for, or the motive power for, the mechanism circulating fluid through the system with which the switch is associated.

A salient feature of my novel flow switch is that it may be used in connection with a system through which a fluid is circulated under pressure or with a system through which a fluid is circulated under suction. To this end a coupling 26 is provided which includes a flange 2| that is adapted to seat against the adjacent end of the housing. Suitable means, such as bolts 22, are passed through the flange 2i and into tapped openings as 23, Fig. 2, in the housing to secure the coupling 20 in position. By referring to Figs. 2 and 3 it will be seen that the coupling 28 may be mounted at either end of the housing H, tapped openings as 23 being provided at both ends of the housing for this purpose. Furthermore, suitable connecting means may be provided permanently at both ends of the housing but it is more economical to provide a transferable coupling such as the coupling 20.

Heretofore it has been explained that when the disc D seats on the valve seat R the globule of mercury in the enclosed tubular housing of the switch M is positioned to close circuit between the contacts as 15. Thus where my switch is to be used with a pressure system and circuit through the contacts as it is to be closed so long as pressure is maintained in the system the coupling 2b is mounted at the 1eft-hand end of the housing H, as viewed in Fig. 2. A pipe 26 is extended into and secured in the collar K of the coupling 29 in any suitable way as by the set screws S, and this pipe 2d communicates with the system in which pressure is to be maintained, as will be more fully explained presently. So long as pressure maintained in the system is effective on the disc D, said disc is held in engagement with the valve seat R. However, the mounting of the lever L and the positioning of the parts carried thereon is such that if pressure is not effective on the disc D, as in event of failure or fault in the system, then the disc will move away from the valve seat R into a position substantially like that shown in broken lines in Fig. 2. When, as has been explained heretofore, the disc D so moves away from the seat R, then the globule of mercury in the enclosed housing of the switch M moves away from the contacts as i 5 and circuit through these contacts is there upon opened.

-When, however, the switch is to be used with a system through which fluid flows under suction, or in which a pressure less than atmospheric is otherwise established, the coupling 20 is mounted at the right-hand end of the housing H, as it is viewed in Figs. 2 and 3, the coupling being shown mounted in this position in Fig. 3. In this instance a pipe, similar to the pipe 24, is secured in the coupling 20 and communicates with the system in which suction is to be maintained. So long as the desired degree of suction is maintained in the system, air pressure effective on the side of the disc D disposed away from the coupling 26 in Fig. 3 holds the disc in engagement with the valve seat R. If for any reason the desired degree of suction is not maintained in the system the disc D pivots away from the valve seat R whereupon circuit through the contacts as it is opened as heretofore described.

'It will be seen that by merely making connection at one or the other of the ends of the housing H, the switch may be arranged to be responsive to either suction or pressure. Thus it is not essential that it be definitely known whether the switch is to be used with suction or pressure for the user of the switch may readily make connection as required, in the present instance by positioning the coupling to suit his needs. Furthermore, since the coupling is detachably secured in position, it may be easily moved from one position to the other and therefore the same switch may be used to be responsive to either suction or pressure and this may be effected without the necessity of any intricate adjustments or variation of the operative means of the switch structure.

Regardless of with which type of system my novel switch is employed it is, of course, pressure that is effective in maintaining the disc D in engagement with the seat R and in order to insure proper operation, free of chatter, I mountthis disc on the arm 9 in such a way that proper seating of the disc is insured, and to this end I provide an opening N in the disc of greater diameter than the rivet M (or an equivalent screw or bolt) and I so arrange the rivet (or its equivalent) that the disc is not tightly c amped against the arm 9. Such loose, or oating, mounting affords sufficient adjustability, or compensatory effect, that the disc D will seat on the seat R in the desired manner and chatter and kindred objectionable operation will be avoided.

Moreover, dust or other foreign matter may interfere with proper seating of the disc and to prevent the passage of foreign matter to the disc, when the switch is used with a pressure system I provide a filter that may be interposed between the system and the switch. In the present instance, I form a pocket 25 in the coupling 20 and a filter F is removably mounted in this pocket. The filter F comprises telescoped flanged sleeves 25 and 25 housing steel wool or like material on which dust and other foreign matter may collect. The steel wool is retained in the sleeves 25 and 26' by the telescoped peripheries of such sleeves and the flanges thereon and by crossed 75.

bars B that may be welded to the faces of the flanges on the sleeves and to each other at the point of crossing. Such arrangement of the filter F tends to prevent surreptitious removal of the steel wool or like material.

The filter F is retained in the pocket 25 by set screws T or the like. As best shown in Fig. '7, the lower end of the pocket 25 is arranged to facilitate insertion and removal of the filter F and it will also be seen that no support for the filter in the pocket is provided other than the set screws T, resort to this arrangement being had to prevent removal of the filter F for the area of the lower end of the pocket 25 is such that if the filter is not installed in the pocket then discharge is afforded through the open lower end of the pocket and the vent thus afforded prevents application of sufficient pressure on the disc D to effect operation thereof.

I have referred to the material in the filter F as being steel wool or like material. This material is to be of such nature that if the switch is used with a system through which fumes flow, then the fumes will condense on the material rather than on operative parts of the switch and in this way the collection of a deposit that might cause sticking of the operative parts of the switch is avoided. Thus while the filter acts as such, in that foreign matter as dust will be collected therein, it also serves or affords a condenser and it is therefore to be understood that the term filter is used herein both in the sense of a true filter and also in the sense of a condenser or, in other words, this portion of the apparatus, in a generic sense, is a collecting means.

When the switch is used with a system in which suction is to be maintained, a filter similar to the filter F may be interposed between the system and the switch, and still another similar filter may be provided on the side of the switch communicating with the atmosphere. In this latter instance a second coupling, like the coupling 28, is substituted for the plate P, which is usually mounted over the open end of the housing H opposite that at which the coupling 25 is secured, said plate being fast in position by bolts 2'! passed into the tapped openings 23, spacing collars 28 being provided between the plate P and the adjacent end of the housing H and about the bolts 2'! to space the plate from the end of the housing. It will, of course, be understood that in connection with a suction system the aforesaid second filter may be used alone or but one filter may be used in either of the aforesaid positions, this being facilitated by reason of the fact that the mounting and arrangement of the filters in both mountings is identical. When provision is made for a filter intermediate a suction system and the switch, it

will be apparent that removal of a filter as F from a pocket 25 will prevent proper operation of the disc D.

' The form of mercury switch, the circuit making and breaking means of my novel flow switch, thus far described is equipped with contacts as 55 at only one end thereof and may be used to control operation of the motive means for the device maintaining the fluid flow through the system or to effect operation of visible or audible signal or the like.

The mercury switch H3 shown in Fig. 4, however, is equipped with contacts as 15' at one end and contacts as H5" at the other end. When a switch of this type is employed it will, when in one of its alternate positions, close circuit to the motive means and when in the other of its alternate positions, it will close circuit to a visible or audible signal or the like or, of course, other arrangement entailing the use of two circuits may be set up, the conductors as C in this instance leading from the contacts as I5 and IE" to a fitting having terminals similar to the terminals !9 from which conductors may be led, through a fitting such as 18, to any desired places for any desired usages.

In the form of the invention shown in Fig. 5 the housing Ha is provided with a valve seat Ra against which a disc Da is adapted to seat. In this instance the disc Da is carried by an arm 9a that depends from a rod ma on which said arm is pivotally mounted, the mounting of the disc Da on the arm 9a corresponding to the above described floating mounting of the disc D on the arm 9. A casing Ila is mounted on a pad [6a about an opening I la in the housing 6a. A plate 29 is suitably secured to the pad lfia and affords the bottom of the housing Ha. An opening 30 is provided in the plate 29 and a lever 3| is pivotally mounted on the underside of the plate 29. One end of this lever rests on the upper end of the arm 5a and the other end of this lever extends into the opening 30. Another lever 32 is pivotally mounted on the upper side of the plate 29 and one end of this lever extends into the opening 36 and is pivotally connected to the adjacent end of the lever 3!, as indicated at 33. A saddle 34 is provided on the other end of the lever 32 and this saddle is adapted to bear against one end of the tubular housing of a mercury switch Ma which is carried by a bracket 35 pivotally mounted in the casing iia, as indicated at 36.

The saddle 34 engages the tubular housing of the mercury switch Ma at the end thereof opposite which the contacts as I5a are arranged. A spring 3'! carried by the plate 28 bears against the tubular housing of the switch Eda at the end thereof at which the contacts as l5a are positioned. The spring 31 so acts on the tubular housing of the switch Ma that said tubular housing is maintained seated in the saddle 34. Furthermore, the spring 3? acts through the tubular housing of the switch I la to urge the end of the lever 32 at which the saddle 3G is positioned downwardly whereby the opposite end of said lever is urged upwardly. This causes the adjacent end of the lever 35 to be urged upwardly wherefore the end of the lever bearing on the lever 9a is urged downwardly, and this tends to urge the disc Da away from the valve seat Ra.

Thus when the coupling 20a is positioned at the end of the housing I-Ia, as shown in Fig. 5, and the pipe 24a leads to a system in which pressure is to be maintained, the disc Da will remain seated on the valve seat Ra so long as the pressure is effected thereon, but upon failure of the pressure the spring 3'! will pivot the disc Da away from the valve seat Ra. When the switch Ma is arranged as shown in Fig. 5, such pivoting of the disc Da away from the valve seat Ra will cause the globule of mercury in the tubular housing of the switch 5 4a to move away from the contacts as lea wherefore circuit through these contacts will be opened. If the coupling Zea is arranged at the other end of the housing Ha and the pipe 24a is directed to a system in which suction is to be maintained any failure in the suction will have the effect of breaking the circuit through the contacts as 15a for with the coupling 28a in this position atmospheric pressure effective on the disc Da, so long as suction is effective on the disc, will maintain the disc in engagement with the valve seat Ra against the action of the spring 31, wherefore the globule of mercury in the tubular housing of the switch Ma will close circuit between the contacts as I5a. When, however, suction is no longer efiective on the disc Da, the spring 3'! will pivot said disc away from the valve seat and circuit will be opened between the contacts as l5a.

The coupling 20a has a pocket 25a therein in which a filter Fa (which, as explained above, is also a condenser) is mounted in the manner hereinabove described and, as has been explained, the plate Pa (which corresponds to the plate P) may be supplanted by another filter containing coupling when the switch is used with a suction system if this should be desired.

In the form of the invention shown in Fig. 6, the housing H?) is provided with a valve seat Rb on which a disc Db is adapted to seat. In this instance the disc Db is mounted on a rod V that extends through a bearing Z in the spider W that is mounted in the housing Hb. If desired, a bracket unitary with the housing may be used in place of the spider W. Such mounting of the disc Db enables the disc to move in a straight line toward and away from the valve seat Rb instead of pivoting toward and away from such a valve seat as in the forms of the invention shown in Figs. 2 and 5.

In the present form of the invention the lever L is pivotally mounted on a rod Ifib carried by the housing Hb. The lever L includes a depending arm 9b, the free end of which is connected to a lug A on the disc Db by a link 38. The arm 213 of the lever L is formed to provide a clamp in which a mercury switch I 4b is secured. The switch I 4b has contacts as l5b therein at one end thereof. An arm 39 projects from the arm I2b in a direction opposite to the positioning of the contacts I5b and a weight M is mounted on this arm 35. The weight 4!! acts through the arm 39 so as to tend to pivot the lever L in a direction such that the disc Db is urged away from the valve seat Rb. However, when the coupling 26b is positioned as shown in Fig. 6 and the pipe 24b leads to a system in which pressure is maintained, the disc Db will remain seated on the valve seat Rb so long as pressure is effective thereon, and when the disc is seated on the valve seat the globule of mercury in the tubular housing of the switch I 4b closes circuit between the contacts as I5b. When, however, pressure is not imparted on the disc Db the weight 40 causes this disc to move away from the valve seat wherefore the lever L so pivots that the switch l -lb is so positioned that the globule of mercury disengages the contacts as l5b and circuit through these contacts is opened.

In this instance the coupling 29b may be mounted at the end of the housing H opposite that shown in Fig. 6, and in the manner heretofore explained this will arrange the switch for use with a suction system, and when the switch is so arranged circuit through the contacts I5b will be maintained closed so long as suction is effective on the disc Db.

The coupling 29b has a pocket 2% therein in which a filter Fb (which, as explained above, is also a condenser) is mounted in the manner hereinabove described and, as has been explained, the plate Pb (which corresponds to the plate P) may be supplanted by another filter containing coupling when the switch is used with a suction system, if this should be desired. In the form of the invention shown in Fig. 8, a

disc Do is mounted in the housing I-Ic to be responsive to pressure of suction in a manner similar to that in which the discs d, Da and Db are so responsive but in this instance the disc does not seat on a valve seat such as the valve seat R. The switch shown in Fig. 8 is particularly useful in those instances where fumes will pass through the system with which the switch is used and particularly where the fumes are of such nature that they are likely to congeal and produce a gummy deposit. It will be noted that clearance is provided around the periphery of the disc Do in the passage in the housing He in which it is mounted so that any fumes which may pass through the filter or condenser Fc into the passage in the housing He may freely flow past the periphery of the disc Do. The form of switch shown in Fig. 8 may be used without a filter or condenser Fc but, of course, the use of such a filter insures against condensed fumes impairing proper operation of the switch.

Inasmuch as the disc D0 is not to seat on a valve seat as 80, it is not necessary to provide a floating connection between the arm and the disc Dc such as the floating connection that is provided between the disc D and the arm 9 or the disc Da and the arm 9a. Instead of this, the rivet Mo firmly connects the disc Do to a pad on the arm 90.

The arm 9 is part of a lever Lc which, like the lever L, is fulcrumed substantially midway between its ends and in this instance the fulcrum is afforded by a rod Illc carried by the housing Ho. The arm 9 extends through an opening He in the housing Ho. The arm I20 of the lever Lc extends through an opening 4| provided in the plate 290 that overlies the opening I I0 and which is secured to the upper face of the pad H60 about the opening a, the lower end of a housing I'Ic being mounted on this pad I60 just as the housing I! is mounted on the I6. The arm l2 carries a saddle I30 in which a mercury switch I40 is removably mounted.

The arm 90 is formed to define a shoulder 42 that is adapted to seat against the underside of the plate 290 when pressure or suction is effective on the disc Do to move it into the position in which it is shown in Fig. 8, in which position the globule of mercury in the housing I40 closes circuit between the contacts as I 50 to which conductors Co are connected, said conductors corresponding to the conductors C. It is the engagement of the shoulder 42 with the underside of the plate 290 that stops the disc Do in the position in which it is shown in Fig. 8. When pressure or suction is not eifective on the disc Dc, the parts are so constructed and arranged that the disc Dc will pivot into a position substantially similar to the dotted-line position of the disc D in Fig. 2 in which position the globule of mercury in the housing of the switch I40 will disengage the contacts I50 to open circuit therebetween.

In the present form of the switch, a coupling 200 is provided which has a pocket 25c therein, corresponding to the pocket 25, and in which pocket a filter Fc, corresponding to the filter F, is retained. The pipe 240 that is connected in the coupling 200 is intended to lead to a source of pressure when the coupling 20c is secured to the end of the housing in which it is shown in Fig. 8 in order that, when pressure is applied on the disc Do, the shoulder 42 will engage the'plate 29c. When, however, the cou- 'plili 20c is-mounted at the end of the housing Hc to which the plate P is connected, as the switch is shown in Fig. 8, and the pipe 240 leads to asourceof suction, then atmospheric pressure effective on the disc Dc, so long as suction iseifective thereon, causes the disc D0 to move into the position in which the shoulder 42 engages the plate 290. It will thus be seen that it is engagement of the shoulder d2 with the plate 29c that serves as a stop to position the disc Dc.

It will, of course, be understood that another coupling, similar to the coupling 200, could be used in place of the plate Pc when the switch shown in Fig. 8 is used with a suction system for the purpose that has been described hereinabove.

In the forms of the invention shown in Figs. 2, 5, 6 and 8 the connection of the pipe as 24 with a system in which pressure is to be maintained causes circuit between contacts as l to be closed so long as pressure is maintained. However, by merely reversing the position of the switch as M, that is to say, by changing the position of the switch in the saddle as l3 so that the contacts as l5 Will be on the other side of the saddle from that in which they are shown, the opposite result could be obtained, which is to say, circuit between the contacts as l5 would be closed rather than opened upon the failure to maintain pressure in the system with which the pipe as 24 communicates. Furthermore, with the switch as I4 positioned as just described the connection with the system may be made at the end of the housing in the manner shown in Fig. 3 in any of these forms of the invention, and under such circumstances the failure of suction would result in closing the circuit between contacts as l5 rather than opening it as heretofore described.

It will also be understood that the switch 14 shown in Fig. 4 may be used in any of the illustrated forms of the invention.

Inasmuch as it is only necessary that the disc on which the pressure is efiective, in the Various forms of my invention, move upon variation in pressure or suction, it will be appreciated that my novel switch need not be arranged in the path of flow through the system with which it is associated, but rather it is only necessary that a pipe as 24 so communicate with the system that the pressure or suction maintained in the system may be effective on the disc without flowing through the housing of the switch.

It will be seen from the foregoing description that I have provided a switch which may be expeditiously arranged to be responsive to either suction or pressure and that likewise this switch may be expeditiously arranged to either close or open a circuit upon failure in the system with which it is used, that is to say, failure to maintain pressure in a system wherein pressure is to be maintained or failure to maintain suction in a system wherein suction is to be maintained. Such universality in my switch is attained by very simple means which do not require any intricate adjustments or particular skill and such changes which are necessary in the switch may be accomplished by the use of simple, readily available tools.

While I have illustrated and described selected embodiments of my invention, it is to be understood that these are capable of variation and modification and I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. In a pressure-suction switch, a housing having a channel therein and similar end portions at opposite ends of the channel, of which a selected end portion remains open in use, means for coupling a pressure communicating pipe to said housing at one end of said channel, said same means being effective to couple a suction communicating pipe at the other end of the channel, a switch actuating member having a pivotal support normally holding the said member positioned in the channel for permitting flow of fluid through the channel and shiftable to a predetermined position intermediate the ends of the channel by pressure effective on one side thereof and by lC'biCIl effective on the other side thereof and 1 so disposed in said predetermined position, 010: 1g the channel to the further passage of fluid therethrough, stop means for effecting positioning of the said actuating member in said predetermined position when either pressure in one direction or suction in the other direction is effective to shift the actuating member from its normal position, switch means under control of said actuating member, said actuating member effecting predetermined operation of said switch means when disposed in said predetermined position, said coupling means including a coupling member open at both ends for communication one end with the housing and at its other end with a pressure-suction pipe, and also havin a wall opening, which side wall opening, when open, vents the interior of the coupling to the atmosphere and prevents effective operation of the switch actuating member, and a filter member in said coupling member for preventing the passage of fumes to the switch means and switch operating means from a pressure-suction pipe connected to the coupling member, and which filter member, when in position within the coupling member, closes the said side wall opening thereof and thus provides for effective operation of the switch actuating member.

2. In a pressure-suction switch, a housing having a channel terminating in oppositely disposed similar ends of which a selected end remains open in use, and also having a slotted side wall opening intermediate said ends, means for coupling a pressure communicating pipe to said housing at one end of said channel, said means being eiiective to couple a suction communicating pipe in a similar manner at the other end of the channel, a switch actuating member including a pressure-suction shiftable disk within the channel intermediate its ends and a supporting arm pivoted in the slotted side wall opening of the housing, with its outer end projecting beyond its pivot and its inner end extending into the channel and in connection with the disk at a point approximately at the center of the latter, said arm normally holding the disk in a position inclined with respect to a right angle to the axis of the channel and freely supporting said disk for movement to a position at right angles to the axis of the channel by pressure on one side thereof as well as by suction on the other side thereof, stop means effective to check movements of the disk from its normal position and to maintain the same when pressure-suction actuated, in said right angular position, and switch means with which the outer end of said disk supporting arm is operatively associated for efiecting predetermined operation of the switch means when the J5 ripheral edge portion of the disk tlieieagainst, and the connection between the innerend of the disk supporting arm and the disk is a'loose-connection permitting the disk to seat evenly against the stop rib.

WALTER J. U'HLHORN. 

